By default, the FilterControl's FilterCriteria property is updated only after the ApplyFilter method has been called, while the ActualFilterCriteria property does not send notifications when the user changes the filter.
This sample project shows how to force an unbound FilterControl to update its FilterCriteria property and bind another control or a view model to this property.
To learn more on how to implement similar functionality in WPF, refer to the E3766 example.